This proposal is divided into four parts. The first part deals with an enantiospecific total synthesis of the C and D rings of VITAMIN D3 and its important hydroxylated metabolites. The second part of the proposal deals with a new synthetic method recently developed in the applicant's laboratory which will be exploited in stereospecific total syntheses of the medicinally important steroids ESTRONE, ANDROSTERONE, PROGESTERONE, TESTOSTERONE and CORTISONE. The third part of the proposal outlines three enantiospecific approaches to the total synthesis of CORTISONE which are mechanistically based on the classic i-steroid rearrangement. The last part of the proposal is based on experiments recently conducted in the applicant's laboratory and outlines an enantiospecific approach to the total synthesis of a new class of natural products which show in vitro antimicrobial activity, mainly the amphilectanes and cycloamphilectanes.